The present invention relates to a support body for an apparatus having an extended nip formed between the support body and a counter-pressure member, said support body having a working surface, and being elastically deformable, and comprising a plurality of pressure chambers that are arranged to be pressurized for controlled expanding in the direction of the working surface in order to load the nip via said working surface.
The invention also relates to a support body assembly for an apparatus having an extended nip N, comprising:                a support body having a working surface, and being elastically deformable, and comprising a plurality of pressure chambers said nip (N) being formed between the support body and a counter-pressure member, said chambers being arranged to be pressurized in order to load the nip (N) via said working surface; and        a holding device for the support body, the holding device providing an outer support to all sides of the support body having said pressure chambers except the side of the working surface so that a pressurization of the pressure chambers cause the pressure chambers to expand in a controlled manner in the direction of said working surface.        
The invention also relates to an apparatus for the treatment of a fibre web being manufactured in a paper or board machine, comprising:                a first structural element, and a second structural element movably arranged with respect to the first structural element and having a counter-pressure surface for interaction with the first structural element to form an extended nip, said first structural element including:                    a movable clothing;            a support body assembly, including                            a support body having a working surface that together with the counter-pressure surface defines said nip, said support body being elastically deformable and comprising a plurality of pressure chambers arranged to be pressurized in order to load the nip via said contact surface; and                a holding device for the support body, the holding device providing an outer support to sides of the pressure chambers except at a side of the pressure chambers facing said working surface so that a pressurization of the pressure chambers cause the pressure chambers to expand in the direction of said working surface.                                                
The previously known presses with an extended press nip have a so-called press shoe, which consists of a metallic material, such as aluminium or steel, and are designed with a press surface, usually a concave press surface, whose profile is very accurately adapted to the opposed counter-pressure surface. Such a press shoe is very complicated to manufacture and therefore involves a very high cost. Due to the fact that it consists of metal, it is relatively rigid and inflexible. The press roll acting as a counter roll such a shoe press can have a relatively thick cylinder wall which withstands the forces from the press shoe. In accordance with another embodiment of the counter roll, it has a relatively thin cylinder wall and is provided internally with a counter-pressure system for adjustable crowning of the thin and, thus, deformable cylinder wall or shell in dependence of the forces the press shoe has to apply on the counter roll in order to obtain the desired load. Also the press shoe can be crowned in accordance with the crowning of the counter roll, and it will then be usable only in combination with this counter roll. Alternatively, the metallic press shoe can be tilted by means of hydraulic cylinders.
A Yankee cylinder has a cylinder wall or shell which is relatively thin, and which easily is deformed by impression of the press shoe when the Yankee cylinder is used as a counter roll. The deformation of the shell varies in an axial direction from the central region in a direction towards the end walls, where the impression is substantially smaller than within the central region. Therefore, the press shoe will act with a higher pressure at and in the vicinity of the end walls, resulting in an increased wear at the edges of the press felt and an irregular load profile along the press shoe, something which in its turn results in variable paper properties crosswise to the machine direction. It has been proposed to crown the shell of the Yankee cylinder by means of an internal counter-pressure system, or to arrange two or more rows of hydraulic cylinders on the underside of the press shoe for influencing the press shoe to conform to the deformed surface, in both cases in order to achieve a more uniform load profile. Both proposals, however, are complicated and expensive to carry out.
The following documents are examples of presses having extended press nips.
DE 44 05 587 and WO 02/44467 describe a press having a hydrostatic bearing, including a press shoe 3 or double press shoes 3a, 3b of the same design. A press belt 6 rotates on top of a lubricating fluid bed of the press shoe 3 with a very small friction. The press shoe, which is made of metal, has a pressure chamber 10 containing a hydraulic fluid, preferably water. A rectangular pressure-equalizing membrane 20, consisting of a suitable solid material, preferably stainless steel, is fixed on the press nip side of the press shoe. The pressure-equalizing membrane 20 has an outer edge 26, an inner edge 22, and an opening 27 that is defined by the inner edge 22. The pressure-equalizing membrane 20, thus looking like a frame, is flexible so that an edge zone 21, standing in direct contact with the hydraulic fluid, can deflect when pressure differences occur between its two sides. These pressure differences arise when hydraulic fluid happens to leak out through the press nip as a result of irregularities in the paper web and/or in the envelope surface of the counter roll. Thus, the flexible pressure-equalizing membrane 20 creates a self-adjusting nip 2, having no or only a minimum of fluid leakage. Thus, through the opening 27 in the pressure-equalizing membrane 20, the pressure fluid in the pressure chamber 10 stands in direct contact with the movable belt. The complementary addition which has been done in said WO-publication in comparison to said DE-publication is that the flexible membrane has been provided with “pinholes 255” within its free edge zone 21 in order to conduct hydraulic fluid from the pressure chamber 10 to the belt 6 for the purpose of lubricating the belt.
U.S. Pat. No. 5,980,693 describes presses having a tube-shaped or inflatable loading element, but with a metal shoe between the loading element and the inside of the belt. Furthermore, this part of the shoe is constructed in order to provide a slow reduction of the pressure in nip outlet. Normally, an abrupt pressure drop is desired.
U.S. Pat. No. 3,839,147 describes a shoe press having two opposed shoes. Each shoe has a metal bottom and sills, sealing against the inside of the belt. The side of the shoe facing the belt is a perforated diaphragm, which causes the pressure of the hydraulic fluid in a pressure chamber to load the inside of the belt directly. The shoe is of a rather complicated construction with various apertures and reinforcements.
U.S. Pat. No. 5,951,824 describes an ordinary shoe having ordinary hydraulic loading elements. The shoe is coated with a soft and durable layer of polymer or rubber in order to reduce the risk of damages to the belt and shoe from paper wads passing through the press nip.
EP 0 575 353 describes a press having a shoe, which is loaded with bellows being arranged inside a metal cover of the shoe, wherein a belt slides around said metal cover.
U.S. Pat. No. 6,334,933 describes a press having a counterpart of metal, which is provided with a plurality of pressure pockets being sealed by a metal plate and hoses, which also can contribute to loading the opposite portions of the press nip.
U.S. Pat. No. 6,387,216 describes a press having an open fluid chamber, over which a belt is running and which is loading the press nip. The chamber is sealed by means of setting the belt under pressure, so that it is tightened over the edges of the chamber.
EP 1 319 744 describes a method for measuring and regulating the nip pressure in a shoe press, crosswise to and along the web, by means of measuring and continuously adapting the hydraulic static pressure in reference points above measurement holes in the press nip.
DE 30 30 233 describes an elastic slide shoe which is attached to a stand of metal. The slide shoe includes a solid body or a hollow body in the form of a hose which can be filled with a pressure medium. The hose is surrounded by an elastic belt which is attached to the metal stand. The hollow body may be divided into chambers which can be pressurized to different pressures. However, a change of pressure in the chamber or chambers does not result in a change of the loading in the nip because of the fact that the hollow body is permitted to expand laterally during every such increase of pressure.
Wo 2005/038129 A1 describes an elastic support body which, in relation to known support bodies, can be manufactured in a more simple way, without any special machining and without any major consideration to the shape of the opposed surface which it is to work against, and which can provide a loading profile in dependence of the pressure in the pressure chamber or pressure chambers in the same way or even in a better way than what is possible with a conventional support body of metal with one or more rows of pressure pockets which are closed by running belt.
It is an object of the present invention to provide an improved elastic support body having inner support arrangement embedded therein which withstands the differential pressure between adjacent pressure chambers, especially at higher differential pressures, in a desired way.
The support body according to the invention is characterized in that the support body further comprises a plurality of reinforcing profiles disposed in at least one chamber of said plurality of pressure chambers, the interiors of the profiles being in fluid communication with one another via holes provided between said profiles, a wall of the profile facing said working surface including holes for communicating fluid between the interior of the profile and the chamber in which said profile is located, said plurality of profiles providing an inner support to walls defining said at least one chamber.
The support body assembly according to the invention is characterized in that the support body is designed in accordance with any one of claims 1-12.
The apparatus according to the invention is characterized in that the support body assembly is designed in accordance with claim 13 or claim 14.
The expression “nip” is to be interpreted in its broadest meaning in order to encompass such a nip that is defined by a wire and support body.